Field assessment operations employ very large server-side map-image databases (collected by satellite, aerostat, UAV and/or airplane) with increasing frequency. The images are used for visual assessment of ground conditions, navigation and situational awareness. However, the size of such map-image databases make them impractical for use on mobile computing devices due to (1) CPU and data storage constraints, and (2) data transfer constraints.
Mobile computing devices have a relatively (compared to personal computers, workstations and servers) slow CPUs and small data storage capability. For example as of the writing of this description, the data storage capability of a consumer level personal computer is measured in hundreds of gigabytes whereas that of a mobile computing device is measured in tens of gigabytes, roughly a 10:1 ratio. Mobile computing devices also follow a roughly 10:1 ratio.
Map-image databases (collected by satellite, aerostat, UAV and/or airplane) are very large relative to the CPU and data storage capabilities of mobile computing devices. For example a 1 meter resolution 24 bit color database covering an area of 300 km×300 km will be approximately 2160 gigabytes, well beyond the capability of any commercially produced mobile computing device. A 20:1 image compression of operationally acceptable quality would yield 108 gigabytes, still beyond the capability of any commercially produced mobile computing device. Even if such databases could be stored on a mobile computing device, the relatively slow CPU capabilities would create poor query and display performance.
While the CPUs and data storage capabilities of mobile computing devices improve from year to year, so do the capabilities of the sensors that produce image databases, with resulting image database size increases keeping pace or exceeding hardware improvements. For example, 1 foot pixel resolution databases are not uncommon for urban areas where just a few years ago 1 meter was the standard. The difference between 1 meter and 1 foot pixels yields a 10× increase in image database size for the same ground area. Indeed, certain urban areas are now available in 0.5 foot pixel resolution (a 40× increase over 1 meter).
This is further compounded by the availability and applicability of multiple image database collected by different sensors, for example true color and color infrared, and image database collected on different dates, for example before and after a natural or man-made disaster. It's not unusual to see 2× to 4× growth in image data storage requirements due to multiple sensors or dates.
The size of map-image databases used in filed assessments is further compounded by the widespread availability of preexisting map-image database from commercial, non-profit and governmental entities. The size of such databases is routinely measured in terabytes and expected to grow by many petabytes in the future. While not all of this preexisting map-image data is applicable to any one field assessment project or activity, the amount of applicable data does grow proportionally to the growth of total map-image data available from governmental and commercial entities.
In addition to the limit created by the CPU and data storage capabilities of mobile devices, the practicality of using very large server-side image databases is further limited by the ability to transmit such image data over to mobile devices, over mobile networks, for example, cellular, satellite, or radio. The later limitations may be due to technical restrictions (available communications bandwidth), commercial restrictions (permitted use of bandwidth) or economic restrictions (cost of transmission).
Google™ Maps Mobile currently uses knowledge of current GPS position to determine which server-side image tiles at the user's current image display settings (image type, zoom detail level, geographic extent) should be transmitted to and stored on the mobile computing device. Google™ Maps Mobile employs client-side caching to a limited extent based on the user's current GPS position and image display selections. In other words, the only image tiles that are cached and available for disconnected use are for where the user has already been and for their past display selections, not necessarily where they will be at future times or for their future display selections.
To summarize, the field assessment requirements for using server side image databases (collected by satellite, aero stat, UAV and/or airplane) in mobile computing devices exceed (1) the CPU and data storage capabilities of such mobile computing devices, and (2) the data transfer capabilities of commercial mobile networks. These gaps are expected to persist into the future.